An examination of the effect of boundary layer thickness on vortex shedding from a square cylinder near a wall

A computational study has been undertaken to examine the effect of boundary layer thickness δ/D on vortex shedding from a square cylinder in proximity to a solid wall. The computations were carried out in a second-moment turbulence modeling framework using a finite-volume technique. The computed results show that, in general, thickening of the wall boundary layer causes wake periodicity to persist for increasingly smaller cylinder-to-wall gap widths, S/D. The nature of the periodic motion changes as S/D approaches the critical value for complete suppression of vortex shedding. Similar to experimental observations, the location at which coupled shear layer motion is first observed shifts downstream of the base region. This shift is characterized by a rise in the shedding frequency and a drop in the time-averaged drag and lift on the cylinder. In addition, the pressure distribution along the lower wall is seen to change significantly due to the reduced size of the recirculation region in the cylinder wake.